KOMO/ABC News(WEST VALLEY CITY, Utah) -- Josh Powell walked into the police interrogation room in the days after his wife vanished appearing nervous and edgy, according to video surveillance released on Thursday by police in West Valley City, Utah.

Powell's wife, Susan Cox Powell, disappeared in December 2009, and has never been found. Authorities combed vast expanses of the Utah desert, searching in deep abandoned mines near where Powell said he had gone camping the night his wife went missing.

Josh Powell was considered a person of interest in the case but was never named as a suspect.

Authorities closed the investigation into Susan Cox Powell's disappearance earlier this year, saying that no new leads had turned up any evidence of what happened to her. Powell killed himself and the couple's two sons in 2012.

But in December 2009, he was brought into the West Valley City Police Department to answer questions about his missing wife. The police have now released tapes from three interviews Powell gave while officers searched frantically for Cox Powell.

"I just don't think she would leave on her own," Powell told the detectives during one interview.

"OK, that's a start. She wouldn't leave on her own. What do you think has happened?" the detective asked.

"I just don't know. I mean, you know, you can sit and speculate, but I don't have any clue."

"What do you think I'm speculating?" the detective asked.

"The closest people to the person are the top suspects," Powell replied.

Powell appeared evasive and sounded unsure as he answered questions. He told police he had taken his sons for a spontaneous camping trip the night his wife disappeared and said that he didn't think his wife would abandon the family.

But police told him that his own children contradicted his story, saying that Susan Cox Powell had come with the family on the camping trip.

Powell, appearing shaken, responded by telling police that sometimes his children lie.

"There is nothing that happened," he said. "She was not with us, and if my kids said that ..."

"So your kids lied? Do your kids lie?" the detective asked.

"Sometimes they do. I mean, if they said she was with us they know that's not true," Powell said. "She was not with us. I did not leave her at the Pony Express," where he said he'd gone camping with his sons.

During the interviews, Powell told police interrogators that his wife had no history of leaving without telling family members where she was going. Powell made his own guess as to his wife's alleged disappearance, saying that she may have killed herself.

"She was suicidal. She was just sad, I guess," Powell said.

"What was she sad about?" the detective asked.

"I wasn't always, I do a lot, but I don't always do everything that she wants, you know," Powell said. "For a while we were all affectionate, but I don't know if she was upset at work...I don't know [at] all."

The videos also show Powell alone in the interrogation room. He can be seen leaning his head against the wall, talking to himself, crying and shaking his head at various times.

At one point, he asked the police if he was a suspect in his wife's disappearance.

"Have I told you you are a suspect?" the detective responded.

"Well, it's felt like it a few times," Powell said.

Toward the end of the interviews, police read Powell his Miranda rights -- a warning against making self-incriminating statements -- and Powell declined to answer any more questions.

"Yeah, let me think about it for a couple of days," Powell said of his decision about whether to keep talking.

"Your wife is missing, Josh, and you want to think about it for a couple of days?" a detective replied.

"I've already answered everything," Powell said.

Powell insisted on having a lawyer before continuing the interrogation with West Valley City police, who never questioned him again for the rest of the search, which lasted nearly three years. Powell continued to deny any involvement in Cox Powell's disappearance until his death in February 2012.